Irradiation Experiments and Magnet Protection Plans at

SPring-8

T. BizenY. Asano, X. –M. Maréchal

SPring-8

OutlineOutline

• Proposal of radiation-induced demagnetization model

• Experimental methods

• Experimental results

• Energy dependence

• Protection plans

High-energy electron causes photonuclear interaction

High-energy electron causes photonuclear interaction

・ (γ , n) (γ , xn) (γ , p)

・ (n , γ ) (n , α)

e- e±

e±

e±

e±

e±

γγ

γγ

γn

・ Electromagnetic shower

Typical radiation-induced demagnetization of Nd2Fe14B magnets

Typical radiation-induced demagnetization of Nd2Fe14B magnets

Sample

Coercivity is the intensity of the applied magnetic field that required to reduce the magnetization to zero after the magnetization of the sample has been driven to saturation.

Coercivity DependenceCoercivity Dependence

Proposal of Radiation-induced Demagnetization

Model

Proposal of Radiation-induced Demagnetization

Model

Magnetic Domain in MagnetsMagnetic Domain in Magnets

Magnetic Domain Domain WallMagnetic Moments

A magnetic domain is a region within a magnet that has uniform magnetization.

Magnetization ReversalMagnetization Reversal

Magnetized Direction

Magnetic Domain

Domain wall

Expansion of Reverse Domain

Reversed Magnetization

Inverse domain nucleate and expand at the defect or the grain boundary where the anisotropy barrier is the lowest.

Inverse domain nucleate and expand at the defect or the grain boundary where the anisotropy barrier is the lowest.

Applied magnetic field

Concept of the modelConcept of the model

The remanence of the irradiated magnets were recovered by remagnetization.

Magnetization reversal is occurred by heat before the crystalline structure is damaged severely.

1. Magnetization reversal caused by thermal fluctuation.2. Magnetization reversal caused by thermal spike like heat

generation.

1. Magnetization reversal caused by thermal fluctuation.2. Magnetization reversal caused by thermal spike like heat

generation.

Heat ProcessHeat Process

Model of radiation-induced demagnetizationModel of radiation-induced demagnetizationModel of radiation-induced demagnetizationModel of radiation-induced demagnetization

Inverse domain nucleate and expand at the defect or the grain boundary where the anisotropy barrier is the lowest.

The coercivity in the grain decreases with temperature rise.

Thermal Fluctuation

Thermal Spike Like Heat GenerationThermal Spike Like Heat Generation

nHigh energy

High energy recoil atoms lose energy predominantly by inelastic interaction (electronic excitation) in a very small volume and produce very high temperature in a very short time.

D. Kanjilal (2001)

Inelastic

Elastic

Model of radiation-induced demagnetizationModel of radiation-induced demagnetizationModel of radiation-induced demagnetizationModel of radiation-induced demagnetization

Thermal Spike Like Heat Generation

Not all inverse domain walls can expand Not all inverse domain walls can expand

Low Coercivity Magnet High Coercivity Magnet

Inverse domain walls expand easily

Inverse domain walls hardly expand and some of them stop

Low coercivity regionLow coercivity region

Inverse domain produced by thermal spike like heat generation

Inverse domain produced by thermal spike like heat generation

Process of radiation-induced demagnetization in the modelProcess of radiation-induced

demagnetization in the model

Thermal Fluctuation

Thermal Spike Like Heat Generation

Magnetic domain (>10μm)

[T>starting temp. of heat demagnetization]

Heat effected region

Spike track (>several nm)

[T>Currie temp.]

Reason of demagnetizationStarting point of magnetization reversal

Lowest point of anisotropy

Spike track

(γ , e )

( n )

Thermal Fluctuation

• Temperature rises in wide area.• Inverse domain nucleates and

expands at the defect or the grain boundary where the anisotropy barrier is the lowest.

• Coercivity decreases in wide area.• Inverse domain wall expand easily in

the low coercivity region.

• Temperature rises in wide area.• Inverse domain nucleates and

expands at the defect or the grain boundary where the anisotropy barrier is the lowest.

• Coercivity decreases in wide area.• Inverse domain wall expand easily in

the low coercivity region.

Thermal Spike Like Heat Generation

• The recoil atom generates heat over the Curie temperature in a very small region and forms core or track.

• The spike occurs both in grain boundary that anisotropy is low and in grain that anisotropy is high.

• The coercivity around the track is kept high because the thermally effected region is very small.

• Not all inverse domain wall expand in the grain that coercivity kept high.

• The recoil atom generates heat over the Curie temperature in a very small region and forms core or track.

• The spike occurs both in grain boundary that anisotropy is low and in grain that anisotropy is high.

• The coercivity around the track is kept high because the thermally effected region is very small.

• Not all inverse domain wall expand in the grain that coercivity kept high.

High coercivity ( or heat resistant) magnetsHigh coercivity ( or heat resistant) magnets Thermal spike like heat generationThermal spike like heat generation

Thermal fluctuation Thermal fluctuation Low coercivity magnetsLow coercivity magnets

Energy Transfer by Neutron Elastic Scattering

Energy Transfer by Neutron Elastic Scattering

EA:KineticenergyofrecoilnucleusA:AtomicmassnumberE0: Kinetic energy of neutron

A EA

at 2 GeV

B (10.8) : 274 MeV

Fe (55.8) : 56 MeV

Co (58.9) : 52.8 MeV

Nd (144.2) : 21.6 MeV

Sm (150.4) : 20.8 MeV

A EA

at 2 GeV

B (10.8) : 274 MeV

Fe (55.8) : 56 MeV

Co (58.9) : 52.8 MeV

Nd (144.2) : 21.6 MeV

Sm (150.4) : 20.8 MeV

Maximum possible energy transfer from a 800 MeV neutron to the recoil nucleus in 2 GeV electron irradiation.Maximum possible energy transfer from a 800 MeV neutron to the recoil nucleus in 2 GeV electron irradiation.

Experimental Methods

Experimental Methods

The experiments of the 2 GeV electron beam irradiation were made at Pohang Accelerator Laboratory.

Accelerator FacilityAccelerator Facility

Irradiation Area（ Beam Dump ）

Irradiation Area（ Beam Dump ）

Magnetic Field Measurement MachineMagnetic Field Measurement Machine

LinacLinac

Magnetic Field Measurement Machine( Cryostat )Magnetic Field Measurement Machine( Cryostat )

Collaboration with Dr. H. S. Lee et. al.

Compare the magnetic field before and after irradiation.

Compare the magnetic field before and after irradiation.

Field above the surface of the magnet is measured by the Hall-probe.

The probe moves into the shield cover during irradiation.

Low Temperature IrradiationLow Temperature Irradiation

Cryostat Configuration of Sample Setup

Experimental ResultsExperimental Results

Thermal FluctuationThermal Fluctuation

Estimation of the temperature Estimation of the temperature generated by the thermal fluctuationgenerated by the thermal fluctuation

Estimation of the temperature Estimation of the temperature generated by the thermal fluctuationgenerated by the thermal fluctuation

Heat demagnetization of the Nd2Fe14B magnet (NEOMAX35EH)

Heat demagnetization of the Nd2Fe14B magnet (NEOMAX35EH)

Starting temperature of heat demagnetization

Little demagnetization

Large demagnetizationCurie Temperature : 590 K

1. Estimation by using the permeance coefficient 1. Estimation by using the permeance coefficient

Radiation-induced demagnetization depends on the permeance coefficient.Radiation-induced demagnetization depends on the permeance coefficient.

Permeance coefficient (Pc) is a function of magnet geometry related to demagnetization.

2 GeV electrons irradiation

Starting temperature of heat demagnetization depend on the permeance coefficient

Starting temperature of heat demagnetization depend on the permeance coefficient

Pc=0.74Pc=1.68

Below the starting temp. of demagnetization

Over the starting temp. of demagnetization 410 K

Just before the starting temp. of demagnetization 450 K

Data sheet from NEOMAX Co.,

The difference of demagnetization appears between 410 〜 450 K. The temperature of thermal fluctuation was 410 〜 450 K.

The difference of demagnetization appears between 410 〜 450 K. The temperature of thermal fluctuation was 410 〜 450 K.

Little demagnetization at R.T.

2. Estimation by using coercivity dependence on heat and radiation-induced demagnetization

2. Estimation by using coercivity dependence on heat and radiation-induced demagnetization

Radiation-induced demagnetizationHeat demagnetization

Coercivity and starting temp. of heat demagnetization is proportional on Nd2Fe14B magnet.

Little demagnetization occurs over this coercivity

Little demagnetization occurs over this coercivity

Thermal Fluctuation Temp. ：　〜 440KThermal Fluctuation Temp. ：　〜 440K

Stabilization to the demagnetization induced by thermal fluctuation

Stabilization to the demagnetization induced by thermal fluctuation

Stabilization technique to heat demagnetizationStabilization technique to heat demagnetization

• The flux of newly magnetized magnets decrease by thermal fluctuation over a long time period.

• The magnets fabricated in high temperature are stabilized before they use to prevent the flux loss by thermal fluctuation. Commonly used stabilization techniques are designed demagnetization by heat or opposite magnetic field.

Stabilization and radiation-induced demagnetization 1

Stabilization and radiation-induced demagnetization 1

Freshly magnetized magnets (NEOMAX35EH) were stabilized thermally （ 24 hrs. exposure ） on different temperature.

Thermal treatment largely increases the radiation resistance. Thermal treatment largely increases the radiation resistance.

The stabilization temperature and the radiation resistanceThe stabilization temperature and the radiation resistance

The radiation-induced demagnetization at the electron number of a 1×1015 Heat Demagnetization

The radiation resistance was enhanced around the stabilized temperature of 410 K 〜 470 K.The radiation resistance was enhanced around the stabilized temperature of 410 K 〜 470 K.

Heat demagnetization does not exceed the stabilized temperature.Heat demagnetization does not exceed the stabilized temperature.

The temperature of thermal fluctuation was 410 K 〜 470 K.The temperature of thermal fluctuation was 410 K 〜 470 K.

NEOMAX35EH

This enhancement of the radiation resistance was observed in another Nd2Fe14B （ NEOMAX-27VH)

magnet.

This enhancement of the radiation resistance was observed in another Nd2Fe14B （ NEOMAX-27VH)

magnet.

Coercivity : 2864 kA/m

Stabilization and radiation-induced demagnetization 2

Stabilization and radiation-induced demagnetization 2

Demagnetization induced by applying opposite magnetic field is also enhanced the radiation resistance.Demagnetization induced by applying opposite magnetic field is also enhanced the radiation resistance.

Thermal fluctuation is one of the reason of the radiation-induced demagnetization.

Summery of thermal fluctuationSummery of thermal fluctuation

• Several estimations of the thermal fluctuation temperature produced by radiation indicate in good agreement (around 450 K).

• The stabilization technique to decrease the thermal fluctuation was also effective to the radiation-induced demagnetization.

Thermal fluctuation is realThermal fluctuation is real

Thermal Spike Like Heat Generation

Thermal Spike Like Heat Generation

Thermal Spike Like Heat GenerationThermal Spike Like Heat Generation

• The recoil atom generates heat over the Curie temperature in a very small region.

• Not all inverse domain wall expand in the grain that coercivity kept high.

• The recoil atom generates heat over the Curie temperature in a very small region.

• Not all inverse domain wall expand in the grain that coercivity kept high.

Radiation-induced demagnetization is also observed in the heat resistant magnets of SmCo5, Sm2Co17.

Radiation-induced demagnetization is also observed in the heat resistant magnets of SmCo5, Sm2Co17.

Starting temperature of heat demagnetization : 520 K 〜Starting temperature of heat demagnetization : 520 K 〜 > Thermal fluctuation temperature

: around 450 KThermal fluctuation temperature : around 450 K

Thermal spike like heat generation can explain this phenomena.

Mobility of the domain wallMobility of the domain wall

Nucleation Type Pinning Type

Inverse domain wall is pinned Inverse domain wall is pinned Inverse domain wall expand easilyInverse domain wall expand easily

SmCo5 , Nd2Fe14B Sm2Co17

Applied magnetic field

obstacles

Nucleation TypeNucleation Type

Hcj

796

Hcj

8361623676

Pinning TypePinning Type

Large DemagnetizationLarge Demagnetization A Little DemagnetizationA Little Demagnetization

Radiation-induced demagnetization depends on the mobility of the domain wall.Radiation-induced demagnetization depends on the mobility of the domain wall.

Mobility of the domain wall and the radiation-induced demagnetization

Mobility of the domain wall and the radiation-induced demagnetization

These two type of magnets show approximately same thermal properties.

Radiation-induced demagnetization under low temperature

Radiation-induced demagnetization under low temperature

The resistance of radiation-induced demagnetization increases with lower the temperature.

The resistance of radiation-induced demagnetization increases with lower the temperature.

Nd2Fe14BNEOMAX50BHWithout thermal treatment

Hcj 3060 kA/m

Hcj 1116 kA/m

Coercivity increases at low temperatureCoercivity increases at low temperature

The coercivity increases with lower the temperature.The coercivity increases with lower the temperature.

The temperature coefficient of the coercivity of Pr2Fe14B （ 53CR) is larger than that of Nd2Fe14B （ 50BH 、 35EH).

The temperature coefficient of the coercivity of Pr2Fe14B （ 53CR) is larger than that of Nd2Fe14B （ 50BH 、 35EH).

T. Hara, T. Tanaka, H. Kitamura, T. Bizen, X. Marechal, T. Seike, T. Kohda, and Y. Matsuura,: “Cryogenic permanent magnet undulators”, Phys. Rev. Spec. Top.: Accel. Beams 7, 050702-1-050702-6 (2004)

The magnets with high coercivity enhanced by the low temperature were more sensitive to the radiation than the one attribute to the Dy additive.

The magnets with high coercivity enhanced by the low temperature were more sensitive to the radiation than the one attribute to the Dy additive.

27VH Hcj 2864 kA/m (Dy)27VH Hcj 2864 kA/m (Dy)

53CR Hcj 5000 kA/m (temperature 90 K)53CR Hcj 5000 kA/m (temperature 90 K)

50BH Hcj 3060 kA/m (temperature 145 K)50BH Hcj 3060 kA/m (temperature 145 K)

35EH Hcj 1989 kA/m (Dy)35EH Hcj 1989 kA/m (Dy)

Two demagnetization mechanisms under low temperature

Two demagnetization mechanisms under low temperature

Thermal FluctuationThermal Fluctuation

Thermal Spike Like Heat GenerationThermal Spike Like Heat Generation

Magnetic Domain

Around Spike Track

Coercivity Temperature

: Coercivity enhanced by low temperature

: Coercivity enhanced by Dy additive

Same DemagnetizationSame Demagnetization

Different DemagnetizationDifferent Demagnetization

ΔT is very high

Thermal spike like heat generation is the main reason for the demagnetization at low temperature.

Thermal spike like heat generation is the main reason for the demagnetization at low temperature.

・ Thermal fluctuation < Starting temperature of heat demagnetization (estimated <290 K) (340 K for 50BH).

・ Different demagnetizations were observed on the magnets with same magnitude of coercivity generated by different mechanism.

・ Thermal fluctuation < Starting temperature of heat demagnetization (estimated <290 K) (340 K for 50BH).

・ Different demagnetizations were observed on the magnets with same magnitude of coercivity generated by different mechanism.

The magnet that coercivity enhanced by low temperature was much influenced than the Dy additive one.

The magnet that have large coercivity coefficient was more sensitive to radiation even if the temperature was very low.

Energy DependenceEnergy Dependence

Experimental Method

The electron beam energies were varied 4-8 GeV

The electron beam energies were varied 4-8 GeV

Synchrotron in SPring-8

Sample setupSample setup

Magnet samples were thermally stabilized to reduce the effects of thermal fluctuation.

Dependence of magnetic field loss on the electron –beam energy

Dependence of magnetic field loss on the electron –beam energy

Magnetic field intensities decrease with the number of electrons

Magnetic field change rate is not proportional to the beam energy

The radiation-induced demagnetization grew keeping its field change profile.

The radiation-induced demagnetization grew keeping its field change profile.

Field change increases with irradiated electron numbers

The profiles normalized by maximum change show same profile.

8 GeVProfile

The profiles of the magnetic field change that demagnetized at a 2 % with a 4 GeV and 8 GeV electron irradiations.The profiles of the magnetic field change that demagnetized at a 2 % with a 4 GeV and 8 GeV electron irradiations.

The profiles were approximately same.

Protection PlansProtection Plans

SPring-8 Storage RingSPring-8 Storage Ring

• High coercivity magnets ( NEOMAX35EH 1989 kA/m)

•Stabilization ( thermal treatment 415 K × 24hrs)

Magnet propertyMagnet property

XFELXFEL

Principle of the diamond detectorPrinciple of the diamond detector

The electron beam halo monitor has been developed for an interlock device.The beam tests carried out at the beam dump of the SPring-8 booster synchrotron.

•High radiation hardness•High insulation resistance•Sufficient heat resistance

Configuration of the test DetectorConfiguration of the test Detector

H. Aoyagi et.al. XFEL : 60 nC/sec 3.7×1011 electrons/secHalo Monitor

Linearity of the Output SignalPeak current100 mAAverage current 200 pA

Peak current 10 μAAverage current 　　20 f A

preliminary

H. Aoyagi et.al.

The incident electron of 1.5×103/pulse results in the charge signal of about 25 fC.

CryoundulatorCryoundulatorIn-vacuum undulator

200 W@80KCryocooler

Flexiblethermalconductor

Heater

Supporting shaft

T. Tanaka, H. Kitamura

Future Plan Future Plan

TemperatureTemperature

Cryoundulator PrototypeCryoundulator Prototype

Cryocooler

Flexible thermal conductor

Permanent magnet

Cryoundulator PrototypePM Material: NEOMAX50BHu=15mm,L=0.6m

Temperature ControlGM-cycle Cryocooler & Sheath Heater